1. Field of the Invention
The invention relates to the control of oil and gas wells using a plunger lift device and more particularly to adjustable control of such wells.
2. Background
Several technologies are used to assist the production of fluids from crude oil or natural gas wells. One of these involves the use of a plunger, a free moving rod or sealed tube with loose-fitting seals to prevent fluid bypassing between the plunger and the production tubing wall. The plunger is left at the bottom of the well until sufficient pressure has built up to allow the plunger to rise to the top of the well head, pushing the accumulated fluid ahead of the plunger. Movement of the plunger is normally controlled by opening a valve at the well head, connecting the tubing to an outlet line, such as the sales line or in some cases separation equipment used to separate oil, water, and gas. The principle of operation is based on the well slowly building up bottom hole pressure from fluids and gas passing from the formation into the well. When the sales valve is opened, the pressure in the sales line or separator is lower than the bottom hole pressure, so that the pressure differential causes the plunger to travel to the surface. In some instances it is desirable to leave the sales valve open for a period of time after the plunger has arrived at the surface. This time period is frequently referred to as "Afterflow." There are several conditions under which it is desirable not to operate the sales valve for safety or production efficiency reasons. For example, the sales line pressure might be so high that one would not want to try to force more fluid or gas into an already loaded system. Conversely, a low sales line pressure could suggest a broken or ruptured pipe.